Maryland Native Keystone Plants

Juglans nigra – Black Walnut

Information on Growing Habit

Juglans nigra, or Black Walnut, is a keystone plant in Maryland. Reaching a height of 75 feet as well as a 75-foot spread of its branches, growing a foot or two a year. Growth rate can depend on soil, light, and water. Though it will grow thinner and taller in a forested area, reaching a maximum height of 150 feet. Dark gray bark is ridged in a diamond pattern and the leaves are alternate, pinnately compound and have 13-23 leaflets. Insignificant flowers bloom in spring, being pollinated by themselves or by the wind. Black Walnut trees begin producing walnuts within 12 to 15 years. In autumn, the leaves will turn bright yellow and they will start dropping green walnuts. A distinctive, spicy odor emanates from crushed leaves, stems, and shells.

What makes this a Keystone Plant?

125 Lepidoptera species use Juglans species as a host plant including the Banded Hairstreak, Luna Moth, Regal Moth, Imperial Moth, and Walnut Sphinx Moth. This makes it a top 30 Keystone Plant for butterfly and moth caterpillars. The National Wildlife Federation has a great list of other keystone species for the Eastern Temperate Forest. Besides being a host plant, the nuts are an important source of food for the Eastern Fox Squirrel, flying squirrels, woodpeckers, and some other species of birds.

Black Walnuts are also edible for humans! Check out the Feral Forager for tips on preparing and using the nuts. While English Walnuts are more readily available, Black Walnuts have more health benefits.

Juglone Information

Black Walnuts have a bad reputation because it releases a chemical (juglone) into the soil which can suppress growth of plants in its immediate vicinity. Juglone appears to affect non-native ornamentals and vegetables the most. Many of our native plants are tolerant of this chemical because they co-evolved with Walnuts. Check out this list of tolerant plants published by Penn State Extension. Please note some of the plants on the list are non-natives we would not recommend.

Plant Information

Common Name: Black Walnut

Type: Tree

Family: Juglandaceae

Height: 50.00 to 75.00 feet

Spread: 50.00 to 75.00 feet

Bloom Time: May to June

Bloom Description: Yellowish-green

Sun: Full sun to part shade

Water: Medium

Maintenance: Medium

Suggested Use: Shade Tree

Flower: Insignificant

Leaf: Fragrant

Fruit: Showy, Edible

Tolerate: Rabbit, Drought

Information from Maryland Biodiversity Project, Towson University, and North Carolina Extension.